On Thu, 17 Sep 2020 at 07:34, Andreas Schwab [off-list ref] wrote:

On Sep 17 2020, Arnd Bergmann wrote:

quoted

The errno man page says they are supposed to be synonyms,
and glibc defines it that way, while musl uses the numbers
from the kernel.

glibc also uses whatever the kernel defines.

That's right, and from my investigation this isn't a libc issue. The
various libc flavours simply try to follow POSIX and the PPC ABI and
aren't doing anything wrong.

See errno.h for example (https://man7.org/linux/man-pages/man3/errno.3.html):
  EDEADLK: Resource deadlock avoided (POSIX.1-2001).
  EDEADLOCK: On most architectures, a synonym for EDEADLK.  On some
architectures (e.g., Linux MIPS, PowerPC, SPARC), it is a separate
error code "File locking deadlock error".

The root cause is unique to the Linux PPC code in
arch/powerpc/include/uapi/asm/errno.h:
  >/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
  >#ifndef _ASM_POWERPC_ERRNO_H
  >#define _ASM_POWERPC_ERRNO_H
  >
  >#include <asm-generic/errno.h>
  >
  >#undef  EDEADLOCK
  >#define EDEADLOCK       58      /* File locking deadlock error */
  >
  >#endif  /* _ASM_POWERPC_ERRNO_H */

It includes "<asm-generic/errno.h>" to pull in various definitions but
has the side-effect of redefining EDEADLOCK to a non-ABI value which
conflicts with the libc errno.h, as I outline in the patch
description. Other arches which also use different EDEADLOCK and
EDEADLK values (mips,sparc) do not do this. They define EDEADLOCK
*once*, with an ABI-consistent value, and don't have the same issue.

The problem goes back a ways (as Arnd points out), affecting current
stable and all LTS branches, so would be nice to get this sorted out.
I'm certainly interested if there's a better way than proposed in this
patch.

Andreas.

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Andreas Schwab, schwab@linux-m68k.org
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